1. Field of Invention
The present invention relates to the field of electron field emission cold cathodes which have atomically sharp tips and to a fabrication method for making such cathode emitters by fabrication of the gate before the field emitters.
2. Description of Prior Art
Field emission sources require sharp electron emitter structures to create electric field enhancement which promotes electron emission from the tip of the field emitter. The very sharp structures that are required for field emission cathodes have been primarily fabricated by two approaches. The first approach typically starts with a silicon wafer and uses anisotropic crystallographic etching techniques or isotropic etching techniques in combination with oxidation sharpening to form sharp field emitters. A gate structure for modulating the emission current is fabricated after the tip is created. This approach suffers from nonuniform characteristics of the sharp tip due to nonuniform etching and oxidation processes which results in poor uniformity in the tips' radius of curvature.
The second approach uses selective deposition of metals to form conical shapes. In this approach, the gate electrode is formed prior to cathode fabrication. However, following emitter material deposition, this layer of material which exists over the gate electrode is removed from atop the gate electrode. Since the emitter is formed of polycrystalline material using this technique, each emitter tip is different due to random fluctuations of the size and shape of the polycrystallites that make up the field emitter which leads to nonuniformities in the electron emission characteristics.
The Kumar U.S. Pat. No. 5,341,063 discloses cold cathode field emitters comprising an electrically conducting metal layer with diamond field emission tips protruding above the metal. Kumar's fabrication includes the steps of coating a quartz or another substrate with a film of artificial diamond 50-500 nm thick preferably with (111) orientation with a plurality of diamond tips less than about 1 micron apart; depositing a conductive metal over the diamond layer; covering the diamond tips; and etching a portion of the conductive metal to expose the diamond tips with negative electron affinity material.